Dysprosium, at Stage 12, feels independent but under constant attack. Brave people who challenge the world with new ideals. Sometimes they can get such a battering that they feel like giving up. That point -giving up the fight- marks the transition to the next stage in Holmium, where they can no longer preserve their autonomy and have to take a step back. This is felt as a heavy defeat.
Hence the bitterness.
In Erbium, (Stage 14) they have really lost the fight. They feel powerless. After that comes the despair of Thulium (Stage 15) a state so dark it would frighten you to even read about it! Beyond that lies dissociation and ultimately - madness)